01 – HEAVY MINERALS AND ZIRCON MORPHOLOGY: PROXIES BETWEEN RONDON DO PARÁ BAUXITES AND ITAPECURU ROCKS

Ano 09 (2022) – Número 01 Artigos

 10.31419/ISSN.2594-942X.v92022i1a1YKK

 

 

Heliana Mendes Pantoja¹*, Marcondes Lima da Costa²

¹Graduating Program for Geology and Geochemistry (PPGG), Geosciences Institute/Federal University of Pará, Belém (Pará), Brazil, lanampj@gmail.com.

²Geosciences Institute/Federal University of Pará, marcondeslc@gmail.com

*Corresponding author

 

ABSTRACT

The Eastern Amazon bauxite districts are located in the domain of the sedimentary rocks of the Itapecuru Group, which are considered to be their probable parent rocks. To assist in the elucidation, it was investigated the heavy minerals from Rondon do Pará bauxites. The assemblage is formed by ultrastable minerals, both in the Itapecuru and in the bauxite in similar concentrations: zircon, tourmaline, rutile and staurolite. They showed wide varieties of shapes, textures and structures, particularly for zircons, that suggest different sources of provenance. The euhedral zircons in general display the bipyramids {101} and the prisms {100}, which correspond to the S and P zircons, indicative of alkaline granites as source rocks for the Itapecuru, and that in turn are in the bauxite profile. Zircon ́s cathodoluminescences also similarly indicate different sources. They also exhibit variable concentrations of Zr, Hf, Th, U, Nb and Y, but the Zr/Hf ratios are quite constant. Therefore, the Zr/Hf ratios and the do-main of S-types and P zircons, both in the Itapecuru and in the bauxites, demonstrate that in fact its rocks, specifically those that occupied the current bauxite profile, were their parent rocks, thus strengthening the link between the two, bauxite and Itapecuru rocks.

Keywords: cathodoluminescence; typology of zircon; zircon chemistry.

 

INTRODUCTION

Zircon is an accessory mineral very common in most rocks and is very stable in the face to weathering and metamorphism (Martins et al, 2014). Along with other heavy minerals it is classically used to assist in the indication of potential source rocks and consequently the region of provenance. Its high stability allows that its diverse morphological features, developed under different conditions; and characteristics of formation to favor inferring its environmental source (Pupin, 1980; Varvra 1990; Corfu et al. 2003; Köksal et al, 2008; Dill et al, 2012; Li et al, 2014; Martins et al, 2014). From these morphological features Pupin (1980) developed a classification based on the varieties or morphological types of zircon and their possible relations with the formation environment in order to identify the source rocks of this mineral. Other studies have explored the combination of different aspects of zircon, external and internal morphology as an additional component to differentiate its sources of origin (Corfu et al. 2003, Köksal et al, 2008; Shahbazi et al. 2014; Horbe et al. 2013; Martins et al. 2014). Recently, zircons were mainly dated due to these characteristics to determine sources of provenance, source area, age of rocks to assess the contribution of some of them to the formation of bauxites, laterites or karsts in China in recent years (Deng et al., 2010; Gu et al., 2013, Zhao & Liu, 2019). The morphological characteristics now it has been supported by U-Pb geochronological dating, Hf and Lu-Hf isotopes in this mineral. However, the technique of morphology of zircon crystals and the spectrum of heavy minerals has been little explored to identify parent rock of lateritic bauxitic formations, both in the past and in the most recent research. The bauxites of the Paragominas Bauxites Province are well geologically investigated and considered lithologies of the itapecuru Group as parent rocks. In order to demonstrate the importance of this unit’s lithologies, as parent rock, we carried out a heavy mineral study having as main subject the morphological and chemical characterization of zircon of the bauxite-bearing laterite profile from Rondon do Pará and rocks of the Itapecuru Group, taking as example, the laterite profile exposed in the Ciriaco pilot mine.

This study intends to demonstrate, what kind of the lithologies of the Itapecuru Group, were the main parent rocks of the laterite-bauxitic profiles in Rondon do Pará.

 

Location and geological setting

The denominated Paragominas Bauxite Province (PBP) comprises several large deposits, aligned in the north-south direction between Açailândia (Maranhão) and Ipixuna (Pará) (Kotschoubey et al., 2005a,b), among which the Rondon do Pará, in the municipality of the same name stands out, in the southeastern portion of the Province (Fig. 1).

 

The bauxites are found in the domain of Cretaceous siliciclastic rocks of the Itapecuru Group, in addition to those of the Ipixuna Formation, of the Grajaú Basin (Rossetti, 2001), as the main substrate, which in turn overlap the Paleozoic siliciclastic rocks of the Basin of the Parnaíba in general deposited on a crystalline base constituted by Proterozoic igneous and metamorphic rocks of the Gurupi, Tocantins-Araguaia and Borborema Province (Amazon Craton and Gurupi) (Rossetti, 2001). According to Kotschoubey et al. (2005a.b), the lateritic formations of the central and northern portion of the PBP developed from these Cretaceous rocks. The Itapecuru Group is formed by friable kaolinic sandstones, interstratified with clays and levels of conglomerates, siltstone, reddish clays and intraformational breccias deposited in an estuarine-lagoon system (Góes, 1981; 1995; Rossetti et al., 1997; Rossetti & Truckenbrodt, 1997; Kotschoubey et al., 2005a), which does not differ much from the Ipixuna Formation, with kaolinic sandstones interstratified with mudstones and siltstones deposited in a fluvio-estuarine system (Góes, 1981; Kotschoubey et al., 2005a). At Ciriaco mine, in Rondon do Pará, the exposed laterite-bauxitic profile comprises:

 

The substrate (Figure 2)

By inference from exposures in river valleys and road cuts (Figures 2 A and 2 B) near the pilot mine, siliciclastic rocks correlated to those of the Itapecuru Group occur, such as sandy siltstones and mudstones. Thus, the siltstone mudstones are reddish-brown in color, with apparent flat-parallel and slightly friable laminations, overlaid by massive mudstones that have fossil root impressions, which converge to sandy mudstones with wavy bedding. At the top, sandy mudstones stand out and becomes slightly kaolinic and columnar. The entire package reaches 6 m thick. The current aspect of these rocks reflects the result of tropical weathering at the level of saprolite, that has affect this region.  Even so, it is still possible to clearly observe structures of the original rock

 

The lateritic bauxite profile (Figure 3 A and 3 B)

The lateritic-bauxite profile in the pit is up to 5.5 m in thickness and is constituted from the base to the top by the clayey horizon (in the image it is buried by the avalanche of mud), underwent by very porous and reddish to purple colored bauxite. This is overlaid by a nodular iron-aluminous crust that in its upper portion is disaggregated, in which fragments of it are immersed in a reddish-brown clayey matrix. Considered as a horizon, it was called a dismantled Fe-Al crust. At the top of the profile, ferruginous spherulites of purple to reddish color stand out, supported by a yellowish brown sandy-clay matrix.

The lateritic profile is then covered by a thick sequence of yellow clay material, almost massive, dominated by kaolinite and goethite, equivalent to Belterra Clay (Figure 3) by Sombroek (1966).

 

 

MATERIALS AND METHODS

Sampling, Extraction of Heavy Minerals and Characterization by Optical Microscopy

To carry out the present work, 36 samples were collected representing all horizons of the lateritic profile in two pit walls in the pilot mine of Ciríaco bauxite (Alumina Rondon Project, former Votorantim S/A and currently Nexa Resources). As in the pilot mine there was no exposure of the saprolite additionally, 12 more samples were collected at federal road BR 222 km 130 (Fig. 1), 100 km from the Ciríaco pit, representing the distinct sedimentary facies of Itapecuru rocks, mainly mudstones and siltstones, as possible parent rock for bauxite formation.

 

After the description of each of the 48 samples, the heavy minerals were extracted only in the fraction 0.062 – 0.125 mm, because the larger fraction 0.125-0.250 mm was insignificant. The extracted grains were submitted to cleaning with 10% hydrochloric acid. In addition, the heavy mineral concentrates of the laterite bauxite profile received treatment with 5M NaOH for the extraction of aluminum mineral films (gibbsite and / or kaolinite). The extraction of heavy minerals occurred by decantation using bromoform according to the technique of Mange & Maurer (1992). Approximately 100 zircon grains per sample were selected manually using the concentrates of heavy minerals with the aid of a binocular microscope; and were assembled in polished sections for morphological analyzes. For the general identification of the heavy minerals, the grains were mounted on glass slides with Canadian balsam. The identification and counting of the frequency of transparent grains (approximately 200 to 250 grains/glass slides) were used to determine the mineralogical assemblies, using a petrographic microscope, Zeiss Axiolab 2500.

 

 Micromorphological characterization by SEM / EDS / CL

Individual grains of heavy minerals and polished sections of zircon grains were analyzed in their morphological and chemical aspects, using secondary electron (SE) images obtained by Scanning Electron Microscopy (SEM) and semi-quantitative chemical analyzes by energy dispersive X ray spectrometry (EDS) and cathodoluminescence (CL). All samples were previously coated with gold for about 30 seconds and then analyzed with the aid of ZEISS LEO-1430 high vacuum and Hitachi TM 3000 equipment at low vacuum. The images of the grains in polished sections were acquired with SEM ZEISS SIGMA-VP and Gatan cathodoluminescence model Chroma CL2 coupled. Those analyzes has been carried out at Institute of Geosciences of the Federal University of Pará.

 

RESULTS AND DISCUSSIONS

Heavy minerals and their morphological aspects in the lateritic bauxite profile and lithologies of the Itapecuru rocks

The same species of transparent heavy minerals identified in the horizons of the lateritic bauxite profile were found in the Itapecuru sedimentary rocks at Km 130 of BR 222 (Table 1). The minerals in decreasing frequency are zircon, tourmaline, rutile and staurolite, in addition to garnet and strictly cyanite. Generally, the minerals display a wide variety of shapes, colors and surface textures (Fig. 4).

 

Table 1 – Frequency (%) of heavy minerals identified in Itapecuru rocks of Km 130 of BR 222 and in the lateritic bauxite profile of Rondon do Pará. N = Total number of grains counted per glass slide.

	Samples	Zircon	Tourmaline	Rutile	Staurolite	Cyanite	N
	Laterite Profile
	Iron Spherulites	78	18	3	1	0	200
	Fe-Al Crust	83	15	2	0	0	200
	Bauxite	68	22	8	2	0	250
	Clayey Horizon	58	35	5	2	0	250
	Itapecuru Rocks
	Mudstones	64	25	6	3	2	250
	Siltstones	60	28	7	4	1	250

 

• Zircon

It is the most frequent heavy mineral, generally colorless, however some crystals may be brown, pink or yellow (Fig.4). The crystals exhibit prismatic (short or long), euhedral to sub euhedral shapes with simple or complex bipyramidal endings (Fig.4). Rounded to subrounded grains are less frequent in almost all lithotypes of the lateritic profile and Itapecuru rocks, except in the ferruginous crust and ferruginous spherulites. Euhedral and sub euhedral prismatic forms are common in Itapecuru clays, in the clayey and bauxitic horizons. In general, the grains exhibit fractures, color zoning, inclusions of opaque minerals, cavities and impact marks. Fractured and fragmented grains are more frequent in the ferruginous crust and ferruginous spherulites, reflecting the physic-chemical conditions of formation of these horizons and/or even their original conditions in the Itapecuru lithofacies on which these horizons were established. The characteristics of these zircons are similar to those described by Nascimento & Góes (2007) for Itapecuru rocks (mostly sandstones) and by Nascimento et al. (2007) for Albian sequences, although in area very far from Ciriaco pilot mine. They diverge only in the abundance, as zircon grains are supplanted by tourmaline. When compared to the assembly of heavy minerals of the Ipixuna Formation (James et al., 2018), closest to the area investigated here, the similarity becomes even more striking, since zircon is also the most abundant heavy mineral.

 

• Tourmaline

It varies from green, the most common color, to brownish yellow to dark brown. It is presented as prisms (long or short), euhedral to subhedral or as round or irregular grains (Fig. 4). The investigated grains in turn have inclusions in the form of bubbles, microfractures, worn edges, dissolution (corrosion) and overgrowth (Fig.5A, 5B, 5C), in addition to their typical longitudinal striations. Among the tourmaline grains investigated, no distinction was found between the grains of the lateritic bauxite profile and those of the Itapecuru rocks (Fig. 4). The chemical results obtained by SEM/EDS allows to classify the tourmaline grains as dravite-shorlite (Fig.6). Dravite is often described in the metasedimentary (metapelite and metapsamite) sequence (Costa and Araújo, 1996) and general tourmaline in granitoid rocks of the region, which form the substrate of the São Luis-Grajaú and Parnaiba basins (Nascimento et al., 2007), to the first belong the Itapecuru Group and the Ipixuna Formation and to the second reference the Albian sequences. The electron microprobe analyzes of Albian sandstone tourmalines in the São Luis-Grajaú basin (Nascimento et al., 2007) in terms of Fe and Mg are compared in general terms with the tourmalines analyzed in this work, classified as dravite-shorlite.

 

 

 

• Rutile

It is presented in reddish to brownish grains, rounded to subrounded; some them preserve subhedral prismatic shapes (Fig. 4). Several grains showed superficial features such as grooves, fractures and rounded edges (Fig. 5D, 5E, 5F) and in the same way as zircon and tourmaline do not show dependence on Itapecuru rocks and lateritic bauxite profile.

 

• Staurolite

It occurs in the form of generally irregular grains, angular to subrounded, pale yellow to reddish yellow (Fig 4). Some superficial features are more common, such as conchoidal fracture, rounded edges and nipple texture (Fig. 5H, 5I). In the same way as the other heavy minerals analyzed, there was also no dependence on the source material.

 

Comparative Analyzes

The comparative analysis from the morphological aspects and individual textures of the different grains of heavy minerals revealed great similarity between the grains of the lateritic bauxite profile and the Itapecuru rocks suggesting, therefore, these rocks or equivalent to them as possible sources of provenance. At the base of the profile (clayey and bauxite horizon) is found the highest frequency of euhedral grains also shared by kaolinic and massive mudstone. In turn, towards the top of the profile (ferruginous crust and ferruginous spherulites) aneuhedral to sub euhedral zircons predominate. Some features stand out for their recurrence, such as fractures, impact marks, cavities and grooves. Generally, these fractures present small variations, which are probably related to the mechanical resistance and hydraulic behavior of heavy minerals during transport from the source area to the sedimentary deposition site (Morton & Hallsworth, 1999). According to their external morphology, the zircons suggests more than one source of sedimentary to the Itapecuru Group.

 

Frequency of Heavy Minerals in the Lateritic Profile and Itapecuru Rocks

The frequency is quite variable and did not show depend on the Itapecuru rocks or the lateritic profile, which certainly reflects the granulometric nature of Itapecuru sediments (from mudstones to sandstones): zircon (55-80%), tourmaline (15-35%), rutile (1-8%) and staurolite (2-4%) (Fig.7). The frequency of garnet and kyanite is <1%, detected mainly in Itapecuru rocks. The garnet is certainly less frequent due to be it is more susceptible to weathering, especially lateritic, as is the case here investigated. The increase in the frequency of zircon in the horizons upper to bauxite, is parallel the decrease in that of tourmaline and rutile, however in the same order of magnitude of general variation of these materials (Fig.7). This could also suggest that parental sedimentary rocks corresponding to that section of the profile held this signature, its granulometry was slightly higher (it displays much more quartz grains), which favors the concentration of zircon in the larger fraction, 0.125-0.250 mm. The zirconium contents, which certainly represent the zircon mineral, in both Itapecuru rocks and lateritic profile, tend to vary slightly in the same frequency as the mineral grains in the rocks, especially the coarser ones (sandstones). On the other hand, are antagonistic in the thinner (mudstones), which is obvious, since the zircon tends to be concentrated in the coarse fraction; in the lateritic profile this parallelism is clear in the upper horizons (Fig.7), but only up to the bauxitic horizon, when they are then antagonistic, perhaps due to the better recovery during the separation of the heavy ones, or even due to the fractionation of the mineral according to the granulometry.

 

EXTERNAL MORPHOLOGY AND TYPOLOGY OF ZIRCON

For the analysis of the zircon morphology, Pupin’s methodology (1980) was used, which proposes to differentiate the source of origin of the zircon through the most common morphological characteristics, which are expressed by the combination of pyramids and prisms. According to Pupin (1980), the zircon morphology is directly related to the crystallization temperature and the chemical composition of the magma, as well as its volatiles. Temperature affects the development of the faces of the prisms, while the chemical composition of the magma would control the development of the pyramids. In view of these factors, he proposed a typological classification based on the relative development of the faces (Pyramids {101} and {211} and Prisms {110} and {100}). In this way he proposed 64 types of zircon, which point out the different petrogenetic characteristics of its probable source rock.

In the present work, the shapes of 320 zircons were analyzed, which showed varied typology. In Pupin’s classification (1980) the shapes found in the zircon crystals investigated fit mainly as S-type, and can also be P, D and J (Fig. 8 and 9), both for the Itapecuru rocks and for the lateritic bauxite profile.

The development of the pyramidal form {101} over {211} and the prismatic face {100} over {110} (Fig. 10A) predominates.

 

S-Type zircons and its subtypes (S4, S7, S8, S12, S13, S14, S17, S18, S19, S23, S24) are the most frequent (> 50%) in both samples corresponding to the Itapecuru rocks and lateritic bauxite (Fig. 10B and 10C), independently. The other zircon crystals were classified as type P1, P5, D, J3 and J4, with a frequency <5%. S-type zircon is generally an indicator of calcium-alkaline granites, while P- type and D of alkaline granites (Pupin, 1980). According to Pupin (1980), these typological forms develop from an alkaline or calcium-alkaline granitic composition at temperatures ranging from 750°C to 850°C. Anhydrous and subhedral zircon grains also suggested different source rocks and/or source area, however regardless of the classification the analyzed grains present similar features. This indicates that the Itapecuru rocks had as sources rocks mainly calcium-alkaline granites and subordinate alkaline granites. The respective sedimentary rocks thus originated, with these zircon characteristics, also found in the lateritic bauxite profile, demonstrate the strong affinity of these rocks with the overlapping lateritic profile of Rondon do Pará.

 

 

INTERNAL MORPHOLOGY OF THE ZIRCON BY CATODOLUMINESCENCE

Most zircon grains exhibit euhedral to subhedral crystals but may or may not have concentric zonings along the plane defined by the a-c axes. Based on the variation of luminescence intensities, fracture frequency, in the presence of corroded edges, fragmentation and other intracrystalline features, it was possible to separate approximately 60 grains of zircon into two populations denominated as Zr1, which represents 65% of them and Zr2 with 35%:

 

(I)        Zr1 is characterized by prismatic zircons (long or short) in both Itapecuru rocks and lateritic profile. They are euhedral to subhedral, in sizes ranging from 50 to 100 µm, generally exhibiting strong zoning and nuclei with different luminescence intensities. In general, the texture in zoning shows regular, sharp, consistent bands parallel to the contour of the crystals (Fig.11). These characteristics have been reported as typical of magmatic zircon (Corfu et al, 2003). Long prismatic zircons are structurally similar and have areas in oscillatory bands delimited by well-defined edges. Some grains have a dark to light gray core, but are well individualized in euhedral to subhedral shapes (Fig. 11A, 11B, 11C, 11E, 11F, 11G). Being observed mainly in siltstones (Itapecuru) and in the clayey horizon and in bauxite (laterite profile). Short-prism zircons, on the other hand, have several types of zoning (Fig. 11D, 11H), which suggest different sources of provenance. They are more abundant in mudstone’s (Itapecuru), ferruginous crust and ferruginous spherulites (laterite profile).

 

(II)      Zr2 represents the zircon population with subrounded to rounded shapes with homogeneous texture or with poor zoning (Fig. 11I to Q), in sharp contrast to Zr1. In the case of luminescence, several grains showed variable contrast of light, with some being brighter and others darker. The zoning observed in the investigated zircons is similar to those of the studies by Kiliç (2016) found in gneisses, schists and quartzite cyanite, partly related to the processes of metamictization. They usually occur in all lithotypes, but specially are more abundant in the ferruginous crust and ferruginous spherulites of the laterite profile. This in fact reinforces the idea that the lithology that generated the upper horizons was partially distinguished from those for the lower horizons, as already indicated by the frequency zircon and abundance of the zirconium element.

 

To differentiate zircons from igneous or metamorphic rocks Corfu et al (2003) used mainly the internal texture of the grains. In this sense, zircons from the Itapecuru rocks and lateritic bauxite profile show textures marked by well-developed zoning, which are usually attributed to magmatic origin (Corfu et al, 2003; Li et al. 2014). In contrast, zircons with convoluted zoning and chaotic structure (Fig.11I, N, Q) may indicate that these textures were acquired during the metamorphic process (Corfu et al. 2003).

 

ZIRCON CHEMICAL COMPOSITION

In general, the chemical composition of zircon varies within its body, that is, between the edge and its central part, mainly in terms of Hf, Th, U and Y (Pupin, 2000; Köksal et al, 2008; Li et al, 2014). The zircons investigated in the Itapecuru rocks and in the lateritic bauxite profile showed also these variations between edges and center, clearly. Generally, the edges of the grains present higher content of Hf and Th in comparison to the contents closer to its center (Fig.12). On the other hand, Y and U are variable regardless of direction, therefore without a defined pattern. Although the sampling is not very significant, it showed results consistent with those observed in the cited literature. It is important to note that the content of the elements and their variations are equivalent in both Itapecuru rocks and lateritic bauxite profile.

 

Zircons play a fundamental role in controlling the distribution of zirconium and hafnium and may also have a significant influence on the contents of Y, Th, U and Nb, this is useful for distinguishing zircons from different sources (Belousova et al, 2002; Hoskin & Schaltegger, 2003). The general chemical composition of the zircon crystals shows very variable Y, Hf, Th and U contents. (Table 1). However, the average Zr / Hf ratio is impressive because it shows clearly again that they do not depend on the horizons of the lateritic bauxite profile or the Itapecuru rocks. From the values of these average ratios, it was possible to identify two groups divided into: I. Zr / Hf ranging from 22 to 27 and II. Zr / Hf from 28 to 31. These ratios fit those of zircons contained in granitic rocks (Wang et al. 2010). The two groups can also be identified from the individual data (Fig. 13). Th and U contents are also variable as well as their ratios, which range from 0.86 to 5, but in igneous zircons generally the Th/U ratios are ≥ 0.5 (Hoskin & Schaltegger, 2003).  From the above, it is concluded that siltstone mudstones must have been the main generators of the Bauxite laterite profile of Ciriaco in Rondon do Pará area. Similarly, while using other proxies, Gu et al. (2013), Hou et al. (2017) and Zhao and Liu (2019) successfully used isotopes and zircon grains dating to identify bauxite parent rocks and provenance area in China.

 

Table 2. Average elementary compositions of zircons from Itapecuru rocks and lateritic bauxite profile obtained by EDS (% by weight). The number of analyzes per sample is indicated in parentheses.

	Samples/(N analysis)	Si	Y	Zr	Nd	Hf	Th	U	Th/U	Zr/Hf
	Laterite Profile
	Iron Spherolites / (27)	16	0,6	77	0,6	2,5	0,43	0,13	3,31	30
	Fe-Al Crust / (18)	16	0,4	66	2,5	2,1	0,58	0,16	3,63	31
	Bauxite / (25)	13	0,2	55	4,9	2,5	0,45	0,2	2,25	22
	Clayey Horizon / (20)	14	0,5	56	5	2	0,19	0,22	0,86	28
	Itapecuru Rocks
	Mudstones / (26)	16	0,2	76	0,7	2,8	0,58	0,13	4,46	27
	Siltstones / (18)	13,5	0,4	67	2,1	3	0,55	0,11	5	22

 

 

CONCLUSIONS

The heavy minerals from the Itapecuru rocks and lateritic bauxite profile are characterized by an ultrastable assemblage to the tropical weathering (lateritization) processes, basically consisting of zircon, tourmaline, rutile and staurolite, which showed similar distribution and concentration in both materials. The patterns observed in the morphologies, textures and structures are quite similar, especially among zircons. When compared together with the other minerals in each rock and horizons of the lateritic bauxite profile, it showed that the mudstones/siltstones correlate better with the clayey horizon and with the bauxite and differ slightly in the crusts and ferruginous spherulites. Therefore, it suggests that the lithologies that formed the horizons of the base differ from those that gave rise to the top of the profile. In addition, the Zr / Hf ratios separate zircons into two groups with different average ratios, which show lower values in the lower horizons than those in the upper horizons. The typological classification of zircons showed that the Itapecuru rocks had a source of provenance mainly in granite rocks. The zircons of the lateritic profile revealed the same classification as these rocks, therefore demonstrating there is a strong affinity between them. Obviously, the Itapecuru sedimentary rocks equivalent to those ones from BR 222, were the parent rock of the lateritic bauxite profile from Ciriaco pilot mine, especially the mudstones. These rocks, when submitted to the lateritization events that occurred throughout the Amazon during the Cenozoic, also gave rise to the lateritic bauxite profile of Rondon do Pará, which inherited its heavy mineral assemblage. Future research on the bauxite parent rock that forms the set of deposits in the province of Paragominas may focus on the geochemical and isotopic analysis of heavy minerals with emphasis to zircon as a means of better understanding the source and evolution of the sedimentary rocks that formed these bauxites.

 

Acknowledgments

The authors are grateful to the Brazilian National Council for Scientific and Technological Development (CNPq) for financial support (Project 477411 / 2012-6; Grants: 305015 / 2016-8; 304519 / 2009-0) and INCT-GEOCIAM; Votorantim/Nexas Resources for his permission and support in the field work of the pilot mine, especially to the geologist Dr. Hélcio José dos Prazeres Filho, a great supporter, at that time Votorantim researcher; CAPES for the granting of a graduate scholarship via PPGG and the support of LAMIGA Laboratories at GMGA/IG/UFPA, LABMEV and ITV Vale IG/UFPA.

 

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